Vehicles often include a hydraulic braking system that is configured to reduce the speed of the vehicle and/or maintain the vehicle in a stopped position. Hydraulic braking systems include a master cylinder fluidly coupled to one or more hydraulic cylinders. The master cylinder includes an input shaft, which activates the hydraulic cylinders in response to the input shaft moving in a braking direction. Typically, the input shaft is moved in the braking direction when a user depresses a foot pedal. Each activated hydraulic cylinder moves one or more brake pads against a drum, rotor, or other rotating element to brake the vehicle. Releasing pressure upon the foot pedal, such that the foot pedal moves in a release direction to a deactivated position, causes the input shaft to move in the release direction, which deactivates the hydraulic cylinders and permits the drum, rotor, or other rotating elements to rotate freely.
To reduce the force applied to the foot pedal when braking the vehicle, most hydraulic braking systems are supplemented with a pneumatic brake booster. Specifically, some users find that moving a master cylinder input shaft that is coupled directly to a foot pedal requires the user to impart a force upon the foot pedal that is greater than that which may be comfortably and repetitively applied. To this end, the pneumatic brake booster amplifies the force exerted on the foot pedal such that a user may move the input shaft of the master cylinder with correspondingly less force being exerted on the foot pedal.
In general, the pneumatic brake booster includes a housing, a valve shaft, a shell, a diaphragm supported by a plate, a valve, a filter, and an output shaft to the master cylinder. The diaphragm and plate are connected to the input shaft of the master cylinder, the housing, and the shell. The diaphragm divides an internal cavity of the shell into a booster chamber and a vacuum chamber. The valve separates the booster chamber into an atmosphere chamber and a working chamber. A vacuum side of the diaphragm forms a portion of the vacuum chamber and a working side of the diaphragm forms a portion of the working chamber. Vacuum generated by a gasoline engine or a vacuum pump is coupled to the vacuum chamber, such that the vacuum chamber is maintained at a pressure less than the atmospheric pressure. The valve shaft, which is coupled to the valve and the brake pedal, is configured to open the valve in response to the brake pedal moving in the braking direction. The valve closes in response to the brake pedal moving in the release direction.
When the valve is closed, vacuum is supplied to the working chamber, such that the working chamber and the vacuum chamber are maintained at the same pressure level. Accordingly, the approximately equal pressure on each side of the diaphragm causes the diaphragm to remain stationary.
When a force is exerted upon the brake pedal, the booster amplifies the force, such that the input shaft of the master cylinder is more easily moved. In particular, exerting a force on the brake pedal causes the valve to open. As a result, air from the atmosphere is drawn into the atmosphere chamber, through the filter and the valve, and into the working chamber. The imbalance of pressures between the vacuum chamber and the working chamber tends to move the diaphragm, the plate, the valve shaft, the housing, and the input shaft of the master cylinder in the braking direction. Accordingly, the imbalance of pressure amplifies the force exerted upon the brake pedal making the braking system easier to operate.
Common to all components of a braking system is the need for reliable operation. Accordingly, there is a continuing need in the art to provide a reliable pneumatic brake booster.